Separation of t-amyl alcohol from 1-propanol by azeotropic distillation

ABSTRACT

1-Propanol cannot be separated from t-amyl alcohol by distillation or rectification because of the closeness of their boiling points. 1-Propanol is readily separated from t-amyl alcohol by azeotropic distillation. Effective agents are heptane, ethyl acetate and tetrahydrofuran.

FIELD OF THE INVENTION

This invention relates to a method of separating t-amyl alcohol from1-propanol using certain organic liquids as the agent in azeotropicdistillation.

DESCRIPTION OF PRIOR ART

Azeotropic distillation is the method of separating close boilingcompounds or azeotropes from each other by carrying out the distillationin a multiplate rectification column in the presence of an added liquid,said liquid forming an azeotrope with one or more of the compounds to beseparated. Its presence on each plate of the rectification column altersthe relative volatility in a direction to make the separation on eachplate greater and thus require either fewer plates to effect the sameseparation or make possible a greater degree of separation with the samenumber of plates. The azeotrope forming agent is introduced with thefeed to a continuous column. The azeotrope forming agent and the morevolatile component are taken off as overhead product and the lessvolatile component comes off as bottoms product. The usual methods ofseparating the azeotrope former from the more volatile component arecooling and phase separation or solvent extraction.

The usual method of evaluating the effectiveness of azeotropicdistillation agents is the change in relative volatility of thecompounds to be separated. Table 1 shows the degree of separation orpurity obtainable by theoretical plates at several relativevolatilities. Table 1 shows that a relative volatility of at least 1.2is required to get an effective separation by rectification.

                  TABLE 1                                                         ______________________________________                                        Effect of Relative Volatility on Theoretical stage Requirements.              Separation Purity,                                                                      Relative Volatility                                                 Both Products                                                                           1.02   1.1    1.2 1.3  1.4  1.5  2.0  3.0                           (Mole Fraction)                                                                         Theoretical Stages at Total Reflux                                  ______________________________________                                        0.999     697    144    75  52   40   33   19   12                            0.995     534    110    57  39   30   25   14   9                             0.990     463    95     49  34   26   22   12   7                             0.98      392    81     42  29   22   18   10   6                             0.95      296    61     31  21   16   14    8   4                             0.90      221    45     23  16   12   10    5   3                             ______________________________________                                    

t-Amyl alcohol and 1-propanol boil five degrees apart and have arelative volatility of 1.18 which makes it impossible to separate themby conventional distillation or rectification. Table 2 shows that withan agent giving a relative volatility of 1.65, only 26 actual plates arerequired to get 99% purity.

                  TABLE 2                                                         ______________________________________                                        Theoretical and Actual Plates Required vs. Relative volatilty for             1-Amyl Alcohol from 1-Propanol Separation                                     Relative Theoretical Plates Required                                                                    Actual Plates                                       Volatility                                                                             At Total Reflux, 99% Purity                                                                    Required, 75% Eff.                                  ______________________________________                                        1.3      34               46                                                  1.4      20               35                                                  1.65     19               26                                                  ______________________________________                                    

OBJECTIVE OF THE INVENTION

The object of this invention is to provide a process or method ofazeotropic distillation that will enhance the relative volatility oft-amyl alcohol from 1-propanol in their separation in a rectificationcolumn. It is a further object of this invention to identify effectiveazeotropic distillation agents that are stable and can be recycled.

SUMMMARY OF THE INVENTION

The objects of this invention are provided by a process for theseparation of t-amyl alcohol from 1-propanol which entails the use ofcertain organic compounds when employed as the agent in azeotropicdistillation.

                  TABLE 3                                                         ______________________________________                                        Effective Azeotropic Distillation Agents For Separating                       t-Amyl Alcohol From 1-Propanol                                                Compounds        Relative Volatility                                          ______________________________________                                        None             1.18                                                         Methyl acetate   1.6                                                          Ethyl acetate    1.7                                                          Isopropyl acetate                                                                              1.55                                                         Butyl formate    1.45                                                         Di-tert. butyl formate                                                                         1.45                                                         Methyl pivalate  1.6                                                          Methyl propionate                                                                              1.45                                                         Ethyl propionate 1.6                                                          Acetone          1.45                                                         2-Butanone       1.45                                                         Cyclopentane     1.55                                                         Benzene          1.7                                                          Cyclohexane      1.7                                                          Cyclohexene      1.65                                                         1-Octene         1.65                                                         Octane           1.75                                                         Isooctane        1.7                                                          2,2,4-Trimethylpentane                                                                         1.7                                                          Hexane           1.6                                                          t-Butyl methyl ether                                                                           1.55                                                         Petroleum ether  1.55                                                         Dimethoxymethane 1.6                                                          Nitroethane      1.45                                                         Heptane          1.7                                                          Toluene          1.6                                                          Methyl cyclohexane                                                                             1.65                                                         Tetrahydrofuran  1.55                                                         Ethyl formate    1.65                                                         ______________________________________                                    

DETAILED DESCRIPTION OF THE INVENTION

I have discovered that certain organic compounds will effectivelyincrease the relative volatility between t-amyl alcohol and 1-propanolduring rectification when employed as the agent azeotropic distillation.They are methyl acetate, ethyl acetate, isopropyl acetate, butylformate, di-tert. butyl formate, methyl pivalate, methyl propionate,ethyl propionate, acetone, 2-butanone, cyclopentane, benzene,cyclohexane, cyclohexene, 1-octene, octane, isooctane, hexane,2,2,4-trimethylpentane, t-butyl methyl ether, petroleum ether,dimethoxymethane, nitroethane, heptane, toluene, methyl cyclohexane,tetrahydrofuran and ethyl formate.

THE USEFULNESS OF THE INVENTION

The usefulness of this invention can be demonstrated by referring to thedata presented in Tables 1, 2 and 3. All of the successful agents showthat t-amyl alcohol can be separated from 1-propanol by means ofazeotropic distillation in a rectification column and that the ease ofseparation as measured by relative volatility is considerable.

WORKING EXAMPLE

1. Fifty grams of 1-propanol-t-amyl alcohol mixture and fifty grams ofheptane were charged to a vapor-liquid equilibrium still and refluxedfor two hours. The vapor composition was 78.9% 1-propanol and 21.1%t-amyl alcohol; the liquid composition was 68.3%-propanol and 31.7%t-amyl alcohol. This is a relative volatility of 1-propanol to t-amylalcohol of 1.7.

I claim:
 1. A method for recovering 1-propanol from a mixture of1-propanol and t-amyl alcohol which consists essentially of distilling amixture consisting of 1-propanol and t-amyl alcohol in the presence ofan azeotrope forming agent, recovering the 1-propanol and the azeotropeforming agent as overhead product and obtaining the t-amyl alcohol asbottoms product, wherein said azeotrope forming agent consistsessentially of one material selected from the group consisting of methylacetate, ethyl acetate, isopropyl acetate, butyl formate, methylpivalate, di-tert. butyl formate, methyl propionate, ethyl propionate,acetone, 2-butanone, cyclopentane, benzene, cyclohexane, cyclohexene, 1-octene, octane, isooctane, 2,2,4-trimethylpentane, hexane, t-butylmethyl ether, petroleum ether, dimethoxymethane, nitroethane, heptane,toluene, methylcyclohexane, tetrahydrofuran and ethyl formate.